BOSTON (CBS) – A lot of kids beat the heat this time of year in portable pools. Everything from the small wading pool up to a relatively large portable pool that can hold three or four feet of water. “Because they’re relatively cheap, and they’re easy to assemble and disassemble, they’re really not on the radar screen,” says Dr. Gary Smith, a pediatric emergency physician at Nationwide Children’s Hospital in Columbus, Ohio.

He’s the lead author of a new study that finds that “in this country every summer, a child dies every five days from drowning in a portable pool.” Safety information data from the Consumer Product Safety Commission was reviewed. Between 2001 and 2009, there were 244 serious incidents involving portable pools. Two hundred nine of them resulted in deaths. Smith says, “This is the first time that a study has been done on drowning and other submersion injuries associated with portable pools in this country. Most of these children, about 94 percent, were under five years of age. About three-quarters of the injuries occurred in the child’s back yard.”

In fact, this study in the journal Pediatrics says four out of ten times, parents were actually supervising but let their guard down for a few minutes. “Unfortunately, I have treated many children who have drowned,” Smith says. “And once they have their hearts stop, and they stop breathing, it is very difficult to revive them. If you fall from a piece of playground equipment, you get a second chance very often. Not with drowning. It’s quick. It’s silent. And it’s final.”

Parents have to be aware. Just sitting by the pool isn’t adequate, especially if very young children are involved. Dr. Smith warns that “with toddlers and infants, you want to be in the water at arm’s length so if something happens you can rescue them immediately.”

He hopes this study spurs more interest in protective devices that can be installed, although he adds that “for many owners the devices cost more than the pools themselves. We really need to have the manufacturers step in to see if they make effective and affordable protection products.”